Start-Up Strategy

Modeling of Processes and Reactors for Upgrading of Heavy Petroleum 

FIGURE 8.32 Transient temperature profiles of the two start-up strategies. 

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Mustapha, S., Ashhuby, B., and Azni, I., Start-up strategy of a thermophilic upflow anaerobic filter for treating palm oil mill effluent, Process Safety and Environmental Protection, 81 (4), 262-266, 2003. 

The reactor was tested with the treatment of alcohol solutions in water (ethanol and isopropanol). This products have been chosen due to their thermal stability. With this solutions, a safe starting-up strategy was stablished. A typical experience is described below. 

A new kinetic description of a granulation process and start-up strategy has been conceived for acetotrophic methanogens applied for anaerobic UASB reactors. 

Establish a start-up strategy (identify necessary components, hot gas and flow specifications, heating sequence, etc.) to achieve fast start... 

The results of these tests will be used to validate the heat transfer model. Once the heat transfer characteristics are understood, the model will be expanded to include the effects of using a fuel air combustion mixture to generate the hot gas to heat up the system. An overall start-up strategy will be defined that will achieve rapid start and transition to steady-state operation. The strategy will identify the necessary components, the hot gas flow specifications, and the heating sequence. These data will be incorporated into the design of a 5-kWe engineering-scale fuel processor that will demonstrate a start-up time of 2 minutes or less. 

But even this start-up strategy may be problematic under certain circumstances, as is shown in Figure 4-22. In this case it was assumed that the cooling intensity represented in terms of the Stanton number amounts to only half of the value available for the previous examples. 

At this point the remark made in Section 4.1.3.1 about an optimized start-up strategy for the cooled CSTR shall be explained. The safety technical assessment procedure for the cooled isoperibolic SBR has demonstrated that in the case of correct design a prediction of the maximum reaction temperature is easily possible. This can be utilized for the optimization of the start up of the CSTR. The later steady state operating temperature of the CSTR is defined as the set value for the maximum SBR process temperature. In a next step one of the two reactants of the CSTR process is charged initially. Then the reactor is started as a semibatch process by feeding the second reactant. When the maximum temperature is reached, the feed of the initially charged reactant is started, and the feed streams are adjusted in such a way that the Stanton number of the CSTR is established. This way the initial oscillations are elegantly avoided. 

All the terms in the denominator of Eq.(3-6) are functions of plasma composition which, in turn, depends on the adopted start-up strategy. Then, we proceed considering for simplicity a 50% D-50% He mixture and neglect both the D-T reactions and the partial poisoning of the fuel due to the presence of a-particles and protons. In this case the RHS of inequality (3-5) depends on... 

Fig. 4 Start-up strategy for a device similar to that of case a) of Table I (see also Ref.[2]).

As an example, we show, in Fig.4, the start-up strategy that was found suitable for a device similar to that of the case a) in Table I. 

Start-up strategy. Demonstration is required of the approach by which the reactor is taken from a deeply subcritical state with external heating sufficient to maintain the Pb coolant in a molten state to the nominal fission power level and primary coolant natural circulation flow ... 

The implications of multiplicity on distillation design, synthesis, simulation and control can be critical (Bekiaris and Morari, 1996). Using an acetone-benzene-heptane example, Bekiaris et al. (1993) have illustrated how column profiles may jump from one steady state (99% acetone) to another (93% acetone) for some feed disturbance. Seider and Kovach (1987) performed simulations and experiments on dehydration of sec-butanol and conjectured that the observed erratic column behavior is a consequence of MSS. Moreover, the sensitivity and dynamic characteristics of each steady state may differ and affect column controllability. The existence of MSS raises other problems related with the start-up strategy that would drive the column to the desired steady state. Thus, it is essential to detect all possible steady states of a given column. Since the popular commercial simulators do not have provision to find MSS directly, the aim of this work is to develop a systematic procedure to achieve this. A very recent work in this direction is due to Vadapalli and Seader (2001). 

Dynamic process model was build by PROsimulator (Hammarstrdm, 2002) based on detailed static model and it was used to study the control and start-up strategy. One test run in miniplant was solely devoted to define start-up and catalyst activation procedure. As a result of the runs it was noticed that the miniplant facility is operational in spite of the quite many manual adjustments. Of course that also means that the system has to be staffed with skilful personnel at all times during the operation. On the other hand manual control also means that the operator is aware of the changes in the process, which is beneficial when studying new process configurations. 

The temperature required for ignition of the hydrocarbons over a catalyst, which is termed the light-off temperature, is an important feature when operating an auto-thermal reformer or partial oxidation reactor, because it affects the start-up strategy and time demand. The auto-ignition or light-off temperature under conditions of partial oxidation decreases with increasing carbon number. 

Chen et al. [452] developed start-up strategies for a 3-kWei methane fuel processor through dynamic simulations. The experimental fuel processor is shown in Figure 5.64. It was composed of two heat-exchangers for feed pre-heating, an autothermal reformer, three water-gas shift stages and three stages for preferential... 

All these assumptions do not reflect practical experience and results from numerous other publications. The start-up strategy was unfortunately not explained completely, it was only mentioned that fuel was combusted initially. The start-up time demand of the unit was 37.5 min. This start-up time was reduced by increasing the feed flow rate to double that of the nominal value. In fact, the strategy was to remain at a double fuel flow rate, until the temperature of the second stage preferential oxidation reactor started to rise. Then the feed flow rate was decreased gradually. 

Reactor configurations involved in continuous emulsion polymerization include stirred tank reactors, tubular reactors, pulsed packed reactors, Couett-Taylor vortex flow reactors, and a variety of combinations of these reactors. Some important operational techniques developed for continuous emulsion polymerization are the prereactor concept, start-up strategy, split feed method, and so on. The fundamental principles behind the continuous emulsion polymerizations carried out in the basic stirred tank reactor and tubular reactor, which serve as the building blocks for the reaction systems of commercial importance, are the major focus of this chapter. 

Reepmeyer F., J. U. Repke, and G. Wozny, Time optimal start-up strategies for reactive distillation colunms, Chem. Eng. Sci. 59, 4339-4347 (2004). 

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